Application of Spatial Model for Potential Flood Hazard Susceptibility at Trumon Area, South Aceh Regency of Indonesia

Abstract

Indonesia is currently embarking on a transition from a ‘risk retention’ to a ‘risk transfer’ strategy for managing the impact of disaster events. The risk transfer strategy, i.e., insurance policy and protection, requires high-level preliminary risk assessment, which requires detailed attention and analysis in producing hazard mapping. Improvement of methods requires, preferably, the non-deterministic index method in a GIS environment, to produce reasonably good quality hazard susceptibility mapping. Recently, a new spatial method has been developed to improve the parameterization of the spatial analysis method for watershed-scale flood hazard susceptibility mapping. Those parameters, which include the Topographic Wetness Index (TWI), Rainfall Intensity (R), Distance to rivers (D), Altitude (A), Land use (L), and Soil type (S), configure the proposed method called “TWIRDALS”. The present study aims at testing the spatial model TWIRDALS watershed at the Trumon Area, South Aceh Regency, Sumatra Island, Indonesia. Historical flood events associated with the watershed have escalated over the last 25 years in the Trumon watershed. Several steps of geospatial analysis in this study use multi-temporal satellite imagery from 1995 to 2021 to identify area changes in land use rendering over the watershed. The satellite imagery interpretation reveals a remarkable land use change, particularly of the previously 2130 ha of peatland forest observed in 1996, to become a 10,000 ha palm oil plantation in 2021. This current situation has made the Trumon area the recipient of more frequent floods, i.e., from a five-year return period to an annual event.